From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Horman Subject: Re: [PATCH] netpoll: fix race on poll_list resulting in garbage entry Date: Fri, 12 Dec 2008 08:31:27 -0500 Message-ID: <20081212133127.GB2402@hmsreliant.think-freely.org> References: <20081209210644.GC3785@hmsreliant.think-freely.org> <20081211130728.GB5910@ff.dom.local> <20081211090104.02cab3d4@s6510> <20081211181528.GB10558@hmsendeavour.rdu.redhat.com> <20081212070750.GA4180@ff.dom.local> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Stephen Hemminger , netdev@vger.kernel.org, davem@davemloft.net To: Jarek Poplawski Return-path: Received: from charlotte.tuxdriver.com ([70.61.120.58]:56675 "EHLO smtp.tuxdriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757382AbYLLNde (ORCPT ); Fri, 12 Dec 2008 08:33:34 -0500 Content-Disposition: inline In-Reply-To: <20081212070750.GA4180@ff.dom.local> Sender: netdev-owner@vger.kernel.org List-ID: On Fri, Dec 12, 2008 at 07:07:50AM +0000, Jarek Poplawski wrote: > On Thu, Dec 11, 2008 at 01:15:28PM -0500, Neil Horman wrote: > > On Thu, Dec 11, 2008 at 09:01:04AM -0800, Stephen Hemminger wrote: > > > On Thu, 11 Dec 2008 13:07:28 +0000 > > > Jarek Poplawski wrote: > > > > > > > On 09-12-2008 22:06, Neil Horman wrote: > > > > ... > > > > > When executing napi->poll from the netpoll_path, this bit will > > > > > be set. When a driver calls netif_rx_complete, if that bit is set, it will not > > > > > remove the napi_struct from the poll_list. That work will be saved for the next > > > > > iteration of net_rx_action. > > > > > > > > This could be not enough: some drivers, e.g. sky2, call napi_complete() > > > > directly. > > > > > > > > > > There is good reason for this. Although most drivers only have one NAPI > > > instance per device, and multiqueue drivers have several NAPI structures > > > per device, a few devices like sky2 need to support multiple devices > > > running off one NAPI receive. The Marvell hardware has a common receive > > > interrupt for both ports on a dual port card. > > > > > > This kind of hardware limits usage of netpoll. Only one port can be > > > used with netpoll because netpoll makes assumptions about NAPI > > > association. > > > > > > > There was previously good cause to use __netif_rx_complete instead of > > netif_rx_complete some time ago when multiqueue rx was implemented using a set > > of dummy netdevices. But with the separation of the napi code, there is no > > longer any reason for this to be done. > > > > I just took a quick look, and it appears that sky2 is the last remaining driver > > to use the underlying napi routines. > > Hmm... My grep shows a bit more (mv643xx_eth etc.), plus some > __netif_rx_complete(). > didn't check __netif_rx_complete, but IMHO that falls into the same category. Should be pretty straightforward to fix up. > BTW, I don't know these things, but I wonder if it's always safe to > do one more ->poll() after such _complete? (I mean enabled interrupts > and/or some locking problems.) > There are cases in which doing so may trigger a bug, yes, but in those cases the error would again be in the driver. They scheduled a poll, they should be able to handle the trivial case in which there is 0 work to do, calling netif_rx_complete when appropriate. Neil > Jarek P. > > > > > This patch maintains exactly the same functionality that it previously had, but > > allows for the netpoll patch to be safe with respect to the per-cpu poll_lists > > used by net_rx_action. > > > > Regards > > Neil > > > > > > Signed-off-by: Neil Horman > > > > > > sky2.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/net/sky2.c b/drivers/net/sky2.c > > index 3813d15..84bdc3c 100644 > > --- a/drivers/net/sky2.c > > +++ b/drivers/net/sky2.c > > @@ -2694,7 +2694,7 @@ static int sky2_poll(struct napi_struct *napi, int work_limit) > > sky2_write8(hw, STAT_TX_TIMER_CTRL, TIM_STOP); > > sky2_write8(hw, STAT_TX_TIMER_CTRL, TIM_START); > > } > > - napi_complete(napi); > > + netif_rx_complete(napi->dev, napi); > > sky2_read32(hw, B0_Y2_SP_LISR); > > done: > > > > -- > > /*************************************************** > > *Neil Horman > > *nhorman@tuxdriver.com > > *gpg keyid: 1024D / 0x92A74FA1 > > *http://pgp.mit.edu > > ***************************************************/ > > -- /**************************************************** * Neil Horman * Software Engineer, Red Hat ****************************************************/